target-arm: Implement missing ACTLR registers

We already implemented ACTLR_EL1; add the missing ACTLR_EL2 and
ACTLR_EL3, for consistency.

Since we don't currently have any CPUs that need the EL2/EL3
versions to reset to non-zero values, implement as RAZ/WI.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Edgar E. Iglesias <edgar.iglesias@xilinx.com>
Message-id: 1438281398-18746-5-git-send-email-peter.maydell@linaro.org